forcedeth: fix vlans

For some reason, when rxaccel is disabled, NV_RX3_VLAN_TAG_PRESENT is
still set and some pseudorandom vids appear. So check for
NETIF_F_HW_VLAN_RX as well. Also set correctly hw_features and set vlan
mode on probe.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>